1. Field of the Invention
A certain aspect of the present invention relates to an imaging apparatus.
2. Description of the Related Art
There is an increasing demand for wide-angle imaging apparatuses for applications such as rearview monitors of vehicles. As the angle of view increases, chromatic aberration of magnification and distortion of an optical system increase and it becomes increasingly difficult to design an optical system with small aberration. Therefore, to improve image quality of a wide-angle imaging apparatus, it is necessary to employ image processing. For example, patent document 1 discloses methods for correcting aberration of an image in an imaging apparatus that uses an optical system having chromatic aberration of magnification and distortion. In a method disclosed in patent document 1, coordinate transformation is performed separately on each of R (red), G (green), and B (blue) signals (RGB color components) obtained by an imaging device such as a charge-coupled device (CCD) or a CMOS sensor to correct chromatic aberration of magnification and distortion at the same time. In another method disclosed in patent document 1, chromatic aberration of magnification is ignored and coordinate transformation is performed collectively on the RGB color components to correct only the distortion.
[Patent document 1] Japanese Patent Application Publication No. 2006-345054
Generally, an imaging device includes color filters such as a Bayer color filter array. In the periphery of an image where the chromatic aberration of magnification is large, because of broad spectral characteristics of the color filters, the optical point spread function (PSF) of each color component tends to increase and the resolution (modulation transfer function: MTF) tends to decrease even if coordinate transformation is performed to correct the chromatic aberration of magnification. For example, when an image of an object is captured via an optical system having chromatic aberration of magnification by an imaging device with color filters having spectral characteristics as shown by FIG. 17, the PSF of each of the RGB color components in the periphery of the image increases as shown in FIG. 18 (each cell indicates a pixel) because of the chromatic aberration of magnification and as a result, the MTF decreases. For this reason, as shown in FIG. 19, a blur is seen around the original position of a black dot and the resolution (MTF) is still low even after the chromatic aberration of magnification is corrected by performing coordinate transformation on each color component.